These 9 Add-Ons Will Not Improve Your Car's Performance

There are plenty of DIY tricks and fixes to boost a car's performance—the proper use of fuel-injector cleaner can help, for one example—but adding wings, exhaust-pipe tips, mpg gadgets and extra vents are probably going to do more harm than good. Here are the 9 biggest offenders in performance add-ons, ones that just don't add to your car's performance.

1

To paraphrase a line from an engine design text: "A car is a machine that doesn't have enough performance." That's the impression you might get from seeing the array of aftermarket accessories purported to improve a vehicle's performance in one way or another. Unfortunately, many are of low quality and even lower utility, enhancing neither the vehicle's performance nor its aesthetics. In fact, they can actually make both significantly worse. Come along with us as we tour some of the more dubious aftermarket accessories that see far too many applications.

2
Coffee-Can Mufflers

There is nothing quite as viscerally appealing to gearheads as the sonorous note of a great engine, whether it's a high-revving Italian V12, a big-bore American V8 or a slick Bavarian inline six. But the trend in recent years to install large-diameter, coffee-can-size tips on the tailpipes of small-bore, four-cylinder cars has done nothing to enhance either our audio environment or the performance of said cars. Narrow exhaust pipes that lead to a large-diameter exit are still a source of performance-sapping back pressure. The tips themselves do little more than amplify a typically unpleasant sound without actually improving the pitch.

3
Fake Vents

Once upon a time, when cars had ventilation ports cut into the hood or fenders, they actually provided an escape path for hot or high-pressure air. At some point in the past decade, far too many automakers decided it would be a good idea to apply nonfunctional engine-compartment vents to the fenders of several new vehicles. It didn't take long before an array of aftermarket stick-on variants began to pop up on the fenders of everything from 20-year-old Chevy Cavaliers to brand-new Lexus ES350s. Obviously a piece of chromed plastic will have no functional effect on engine cooling, but all too often these aftermarket versions aren't even applied straight, which makes them look particularly tacky.

4
Big Wings

There's a case to be made for a large rear wing on a Porsche 911 Turbo. For instance, there is always the chance, however remote it may be, that the driver of such a car could take it to a speed (on a closed racetrack only, of course) where the downforce such a device generates could prove useful in sticking the rear tires to the ground. On the other hand, bolting one to the trunk-lid of a mid-1990s-vintage Dodge Stratus or Ford Taurus with the stock front end may actually make things worse for these front-wheel-drive sedans. Many of these spoilers are so malformed that they look like they have melted after sitting out in the sun too long, and are likely to generate far more drag than useful downforce. If the vehicle is actually driven fast enough to generate downforce, it might just unload the front wheels, making most vehicles' inherent understeer even more pronounced.

5
Ground Effects

Through the 1980s and 1990s, race cars that were nominally supposed to resemble production cars started sprouting all sorts of aerodynamic appendages across their front fascias and sides in order to help them slide through the air and generate downforce. The root of many of these designs was in the German Touring Car Championship, and the style eventually migrated to the American Trans Am and other series. Sometime in the 1990s, a few owners of smaller front-wheel-drive coupes—particularly those from Honda, Acura, Toyota and Mitsubishi—began taking inspiration from those racers and applied redesigned front fascias and rocker panels to their road cars. Like rear wings, many of these frontal appendages look like globs of melted clay and have almost certainly never been anywhere near a wind tunnel. That means that they are far more likely to generate speed-sapping drag than performance-enhancing aerodynamics. Many also hang so low that they are susceptible to grinding on driveway lips or parking-lot ramps.

6
Badge Engineering

Automakers are often criticized, and rightly so, for badge engineering. When manufacturers use this approach to expand their lineups, it typically involves installing a different grille, lights and maybe some extra trim on a mainstream vehicle to transform it into a premium model. Some of the more noteworthy examples over the years include the Cadillac Cimarron of the early 1980s and any Mercury of the past decade. While these factory examples can sometimes result in a car that's marginally more attractive or has better amenities than the cars from which they originally derived, this is not typically the case for aftermarket badge engineering. For example, adding Cobra or 5.0 badges to a base Ford Mustang V6—or worse yet, a four-cylinder version—will not make it accelerate any faster than it did when new. Similarly, applying M badges to an old BMW 318 without replacing the powertrain, brakes, suspension and seats will not magically make it run like an M3.

Tornado vortex generators are a prime example of something likely to cause more harm than good. Engineers spend countless hours designing intake-flow paths on engines, including the high-turbulence intake ports that mix air and fuel. However, this process takes place as the air and fuel enter the combustion chamber, when the air no longer has to flow. Introducing turbulence upstream—where vortex generators are typically installed—causes airflow to slow and does nothing to promote fuel mixing.

8
Huge Wheels

In recent years, some of the more popular add-ons for cars both old and new are ever-larger wheels. The trend toward big wheels began in the early 1980s as tire manufacturers developed the first low-profile tires and automakers sought to install larger brakes for better stopping performance. At first, carmakers used 15- and 16-inch wheels, but by the beginning of the 2000s, 18- to 20-inch wheels became commonplace.

There are several tradeoffs to larger wheels, including weight and increased turning radii. Large-diameter wheels increase overall weight, rotational inertia and unsprung weight (the mass beneath the suspension that has to travel up and down as the car moves down the road). The more inertia you have at the corners, the worse the car rides and handles. A lack of physical space in the wheel well also limits the ability to turn the steering wheel, making the car more difficult to maneuver in parking lots. The 24- to 30-inch wheels now available require tires with such low sidewalls that they are also extremely easy to damage on curbs and potholes.

9
Fake Hood and Side Scoops

An internal combustion engine produces power by taking in air, mixing it with combustible fuel and igniting it. If you force in more air and add a corresponding amount of fuel, the result is more power. Hood scoops are often added to cars as a means of passively forcing in more air without using a turbocharger or other mechanism. Unfortunately, this ram-air system only works if the scoops actually have openings for the air to flow through. Solid bodywork shaped like a scoop (without any flow passages) not only doesn't improve power, but actually adds aerodynamic drag, potentially slowing the car down.

Aerodynamics can be further degraded by the addition of scoops along the sides of the car. These are typically mounted either ahead of the rear wheels or on the rear quarter windows. Visually, these are meant to make the car look as though it has either an exotic midengine layout or cooling ducts for the rear brakes. Just like hood-mounted inlets, these act more like an air brake than a performance enhancer and, more often than not, will fool no one.

10
Chrome Skid Plates and Brush Guards

While the vast majority of SUVs purchased over the last two decades have never gone further off-road than a gravel driveway, some drivers do appreciate the delicate art of crawling over boulders. For those who partake in backwoods driving adventures, certain accessories, such as brush guards and skid plates, are imperative. They are used to protect radiators, transmissions, transfer cases and differentials from being penetrated by sharp rocks or other objects.

The surefire way to detect a serious rock crawler from a pretender is chrome. Those that actually venture away from civilization will have their protective plates scraped and banged up, making shiny adornments pointless. Unblemished chrome on such a truck is a sure sign the vehicle has never been used as intended.